Folded POLAR count space for two polarization angles and ten levels of polarization degree. The rates have been artificially scaled to between the different angles for visual clarity. The green lines for both angles represent the polarization degree and the red lines . Thus, we can see how various sets of polarization parameters can be identified in the data. The peaks with a 90° periodicity are the result of POLAR’s square shape, while the visible modulation with a 360° period is a result of the incoming direction of the photons with respect to the instrument’s zenith. By forward-modeling the instrument response, the systematics induced by geometrical effects are properly accounted for.